The present disclosure relates to a high voltage power supply and an image forming apparatus, and in particular to technology for correcting a developing bias voltage.
Conventionally, known is technology for reducing the deterioration of image quality by maintaining a constant level of intensity of an electric field that is generated between a photoreceptor (image carrier) and a developing roller (developer carrier) as a result of applying, to the developing roller, a developing bias voltage that is obtained by superimposing a direct voltage and an alternating voltage, and thereby developing an electrostatic latent image. The foregoing direct voltage and alternating voltage are optimized, for example, according to the magnetic intensity of the developer (toner), and the photosensitive material (for instance, amorphous silicon) forming the photoreceptor surface.
Even when an optimized developing bias voltage is applied, if the distance between the photoreceptor and the developing roller changes due to some cause such as the eccentricity of the photoreceptor during development, the intensity of the electric field generated between the photoreceptor and the developing roller will consequently change. As a result, there is a possibility that excess or deficiency will arise in the amount of developer to be supplied to the photoreceptor. Thus, there is one conventional technology for correcting the developing bias voltage. With this conventional technology, capacitance between the photoreceptor and the developing roller is detected, which indicates the distance between the photoreceptor and the developing roller. In addition, the developing bias voltage is corrected to become a proper value that is associated with an absolute value of the magnitude of the detected capacitance. The proper value is set in advance by being associated with the absolute value of the magnitude of the capacitance based on an experimental value obtained from a test operation and the like.
Nevertheless, the capacitance between the photoreceptor and the developing roller changes not only based on the distance between the photoreceptor and the developing roller, but changes also based on environmental conditions such as the humidity and atmospheric pressure between the photoreceptor and the developing roller. Accordingly, upon correcting the developing bias voltage to become the proper value that is associated with the detected capacitance, there is a possibility that the detected capacitance includes the capacitance that changed due to environmental conditions. In the foregoing case, there is a possibility that the developing bias voltage cannot be appropriately corrected since the distance between the photoreceptor and the developing roller is erroneously determined.
For instance, there is a possibility that the developing bias voltage is corrected more than needed as a result of attempting to move the developer in a distance that is longer than the actual distance between the photoreceptor and the developing roller. Contrarily, there is a possibility that the developing bias voltage is corrected less than needed as a result of attempting to move the developer in a distance that is shorter than the actual distance between the photoreceptor and the developing roller. As a result of the above, there is a possibility that excess or deficiency will arise in the amount of developer to be supplied to the photoreceptor, which in turn will cause the deterioration in the image quality of toner images formed on the photoreceptor.
An object of the present disclosure is to appropriately correct the developing bias voltage for reducing the deterioration in the image quality of toner images formed on the photoreceptor.